1. Field of the Invention
Embodiments of the present invention relate to a semiconductor device which is simply attached to a cooler and is manufactured at a low cost, and more particularly, to a semiconductor device without a cooling base (for example, a copper base) which comes into contact with a cooler and a semiconductor device manufacturing method.
2. Discussion of the Background
In a general semiconductor device, an insulating substrate with a conductive pattern on which a semiconductor chip is mounted is fixed to a cooling base (for example, a copper base) and the cooling base is fixed to a cooler (cooling fin).
In recent years, a method has been used which directly fixes an insulating substrate with a conductive pattern to a cooler (for example, a cooling fin), without passing through a cooling base, in order to reduce manufacturing costs and thermal resistance in a low-power semiconductor device.
This semiconductor device is called a copper-base-less type and the insulating substrate with a conductive pattern is a direct copper bonding (DCB) substrate or an aluminum insulating substrate. In addition, for example, a terminal case in which a terminal is attached to a resin case or a case formed by a transfer mold is used as a package and gel (silicon gel) or epoxy resin is used as a sealing resin.
Three representative examples of a method for attaching the copper-base-less semiconductor device to the cooler according to the related art will be described below.
First, there is a method which screws clamps 52 (two positions) which protrude to the outside of a case 51 of a semiconductor device 500 as shown in FIG. 18 of Infineon, “AN2006-08”, Application Note, V2.0, July 2008 (“Non-patent Document 1”).
Second, there is a method in which holes 55 through which screws pass are formed at both ends (two positions) of a case 54 of a semiconductor device 600 and the semiconductor device 600 is screwed, as shown in FIG. 19 of JP 11-243839 A (“Patent Document 1”).
Third, there is a method in which a hole 58 through which a screw passes is formed at the center of a case 57 of a semiconductor device 700 and the semiconductor device 700 is screwed, as shown in FIG. 20 of U.S. Pat. No. 6,979,204 (Patent Document 2).
In the drawings, reference numerals 53, 56, and 59 indicate an insulating substrate with a conductive pattern.
However, in the semiconductor devices 500 to 700 disclosed in Non-patent Document 1, Patent Document 1, and Patent Document 2, as described above, since the semiconductor device is attached to the cooler only by screws, it is necessary to manage screw tightening torque.
In the semiconductor devices 500 and 600 disclosed in Non-patent Document 1 and Patent Document 1, since the area of the screw portion for attachment to the cooler is a dead space, the external dimensions of the semiconductor devices 500 and 600 increase.
In the semiconductor device 500 disclosed in Non-patent Document 1, when the warping of the surface of a back side conductor 53a of an insulating substrate 53 with a conductive pattern which is not divided is examined, as shown in FIG. 21, the surface warps toward the front side of the insulating substrate 53 with a conductive pattern and the warping is not necessarily concentrically spread from the center of the semiconductor device. A significant amount of warping may occur in a portion 60 that is separated from the center of the back side conductor 53a.
In FIG. 21, reference numeral 61 indicates a contour line and the portion 60 is lower than other portions. As such, when the portion 60 in which a significant amount of warping occurs is separated from the center of the back side conductor 53a, the adhesion between the back side conductor 53a and the cooler is reduced during the attachment of the semiconductor device 500 to the cooler and the contact thermal resistance between the semiconductor device 500 and the cooler increases. In addition, in some cases, a thermal grease is applied onto a contact surface between the semiconductor device 500 and the cooler in order to prevent an increase in the contact thermal resistance. However, in the portion in which a large amount of warping occurs, the amount of thermal grease applied increases and thermal resistance increases.
The semiconductor devices 500 to 700 disclosed in the above-mentioned three patent documents will be described in detail below.
In the semiconductor devices 500, 600, and 700, in an assembly process, a screwing operation is required and torque management for screwing is also required. In addition, it takes a lot of time to perform the screwing operation.
That is, in the semiconductor devices 500, 600, and 700, the semiconductor device is attached to the cooler only by screws and a screwing operation is required. In the assembly process, torque management for screwing is required. As a result, manufacturing costs increase.
In the semiconductor devices 500 and 600, screwing portions are disposed in the outer circumference of the cases 51 and 54. The portions are dead spaces. Therefore, the external dimensions increase.
Since one insulating substrate 53, 56, or 59 with a conductive pattern is directly attached to the cooler, the shape of warping (curve) is not fixed, but varies for each semiconductor device. In particular, in the semiconductor device 500, a significant amount of warping occurs in the insulating substrate 53 with a conductive pattern.
As described above, since the shape of the warping of the insulating substrates 53 and 56 with a conductive pattern is not fixed, it is difficult to manage warping. Therefore, when the insulating substrates 53 or 56 are fixed to the cooler by screws, the adhesion between the semiconductor device 500 or 600 and the cooler is reduced depending on the position of the portion in which a significant amount of warping occurs.